Endemic (non-venereal) treponemal disease is common in humid tropical environments throughout the world. Caused by the spirochaete bacterium Treponema pallidum, it is primarily spread during childhood via contact with open wounds on infected persons, although transmission can also occur via oral mucosa. Osteological signs of long-term infection include periosteal reaction in the lower limbs, as well as extensive destruction of the skeleton in advanced cases.

During the Edo period, Miyako Island, located in Okinawa prefecture, was controlled by Satsuma domain of southern Kyushu. Historical accounts suggest that the lifestyle of inhabitants was affected two-fold – in one hand being exploited for their labor and strategic proximity to the Chinese mainland and in another, because their distance from the political center would have translated into reduced economic returns for the population.

Survey of skeletal remains at the Nagabaka site, which dates to this period, has yielded convincing evidence of treponemal infection. Known geographical spread as well as diagnosis via morphological comparison with available paleopathological literature point to yaws (T. pallidum ssp. pertenue) as the pathogen likely present at the site. Furthermore, incidence of cribra orbitalia at the site provides evidence that health during childhood was possibly affected by poor diet or an unsanitary environment.

Our research presents a case study of treponemal disease at the Nagabaka site and briefly evaluates socioeconomic factors that the island underwent under Satsuma rule. Our findings contribute to a better understanding of the relationship between disease and inadequate living conditions, possibly exacerbated by repressive political rule.

This research was supported by grants from Downing College, Cambridge and the University of Cambridge Overseas Trust Additional Fieldwork Funds